Integrated circuit (IC) packages must be tested after their manufacture, normally at elevated temperatures, which is typically a burn-in process. During that process, it is often necessary to control the temperature of ICs, sensors, and other elements. Techniques for doing so have been widely practiced for many years. The system normally consists of a heater (or cooler), a temperature sensor, and a comparator which applies energy to a heater in proportion to the difference in voltage measured on the temperature sensor as compared to a reference voltage. The energy is applied in the proper direction to cause the difference voltage to be reduced. Temperature control modules and temperature sensors of many types are widely sold for these purposes. A typical application is the control of the temperature of ICs for a burn-in process because of the temperature sensitivity of the ICs.
To achieve more accurate testing results, it is desirable to control the temperature of each individual IC being tested. Within a testing oven without individual temperature control, the actual temperature of each IC can vary due to different rates of convection, heat dissipation, or radiation within the oven. Individual temperature control can be achieved by sensing the temperature of each IC and varying the heat directed to each IC through the use of individual heaters.
Two such examples of sensing and heating individual ICs can be found in U.S. Pat. No. 5,164,661 to Jones and U.S. Pat. No. 5,911,897 to Hamilton. Both Jones and Hamilton disclose a testing socket with a sensor in direct contact with an IC that senses the case temperature of the IC.
As shown in FIG. 10, in Hamilton, a temperature sensor 110 is positioned within an insulated sensor housing 112 such that the sensor 110 protrudes from the housing 112 to contact the outer casing of the integrated circuit being tested. Hamilton discloses measuring the surface temperature (the case temperature) of the IC under test and does not disclose any apparatus or method for determining the temperature of the center of the IC (the junction temperature).
Jones discloses determining the junction temperature of the IC under test by calculating that junction temperature from the sensed case temperature and a predetermined thermal profile of the IC. The determination of the junction temperature of the IC is subject to time delays caused by the thermal time constants of the materials between the temperature sensor on the case surface of the IC and the junction of the IC.
Thus, it would be advantageous to have a system and method for more quickly determining the junction temperature of an IC under test.